Generally, a work vehicle such as a wheeled excavator is provided with a service braking device that provides a braking force when a brake pedal is operated to drive a brake valve. The service braking device can be used as a work braking device upon working. In this case, the service braking device is continuously operated by the operation of a brake switch. That is, the service braking device is hydraulically locked. This type of braking device is disclosed in, for example, the following prior art reference (cf., Patent Document 1).